Oscillating signals are widely used in electronics. Examples of their use include providing clock signals, or providing carrier signals which can later be modified to include information. For example, an oscillating signal can be used to drive a row in a capacitive touch sensor panel. Changes to the sensed signal indicate a touch event at the panel.
There are various known ways to create an oscillating signal. For example, persons of skill in the art would recognize that a simple circuit including an inductor and a capacitor would create such a signal. However, most circuit based oscillators suffer from the fact that they do not provide a signal with a precise and predictable frequency and phase.
Therefore, many electronic devices use crystals to provide an oscillating signal. Crystals are known to provide signals of more precise frequencies. Since it may desirable to generate a wide range of frequencies in a higher frequency band, the crystal may serve as a frequency reference for a frequency multiplier whose output provides a stable frequency which accurately tracks the crystal frequency and can be a multiple of the crystal frequency, the same or lower frequency Such circuit is referred to as a Phase Locked Loop, or PLL. Using a PLL to generate higher frequencies has the benefit of generating accurate and higher frequencies from a crystal based reference clock that's much lower in frequency, potentially easing the requirement on the type of crystal used and lowering power consumption (usually crystals are not offered beyond 100 Mhz and usually, the power consumption of the crystal oscillator scales it's frequency. Therefore, it is desirable to keep the crystal oscillator frequency as low as possible.)
However, the use of crystals adds significant costs to the system not only because of the crystal itself but also because of associated support circuitry and PCB space, which is usually very limited in some devices such as, for example, small hand held products.